It isn’t easy catching up to Yelp’s and TripAdvisor’s huge leads in user reviews so Google was handing out cups and Zagat city guides yesterday to people at the Prudential Center mall in Boston if they would write restaurant and shopping reviews for Google+.

Passersby would sit down, grab a laptop, and write reviews, with Google enticing them to “Live La Vida Local on Google+.”

Dispatching the troops to the mall to hawk reviews is designed to accelerate Google’s efforts to build its base of user reviews on Google+, where the stockpile lags way behind earlier adopters Yelp and TripAdvisor.

It’s a problem that all new-entrants have, although admittedly Google is not your typical new kid in the neighborhood.

Interestingly, Google is emphasizing its need for restaurant and shopping reviews, and not-so-much critiques of hotels, as its signage implores:

Discover and share the right places to eat, drink, shop and play with reviews from Zagat and trusted friends on Google+ Local.

However, with Frommer’s now in the Google fold to supplement Zagat, perhaps hotel reviews will be accorded more importance.

Here’s Google’s problem: It is late to the user review business, having set out on its current course after being roundly criticized in Washington a couple of years ago for taking Yelp’s and TripAdvisor’s user reviews without permission.

If you type “Boston restaurants” into the Google search box, the first listing is for 5 Napkin restaurant at 105 Huntington Ave., and the listing appears in Google+ Local. There are just 19 user reviews for the restaurant, which is rated 15 out of 30, or “fair to good,” in the Zagat scoring system.

Yelp has 284 reviews for 5 Napkin, scoring it 2.5 stars out of 5, and TripAdvisor offers 121 user reviews, and gives it a 3.5 out of 5.

Google hopes handing out swag at shopping malls will help it close the gap.

But, it could also in theory lead to credibility problems for Google because it is handing out merchandise — admittedly not high-end items — and perhaps prompting people to write reviews even if they have never visited the eatery, stayed at the hotel, or bought the product.

No word yet about how Google might incentivize power reviewers. As one observer put it: Will Google hand out cars that can drive themselves in exchange for 20 reviews?